This invention relates to silver complex diffusion transfer process and especially to photographic materials for use in such process.
The principle of the silver complex diffusion transfer process (DTR process) is disclosed in U.S. Pat. No. 2,352,014.
According to the DTR process a silver complex salt is imagewise transferred by diffusion from a silver halide emulsion layer into an image receiving layer, where it is converted to a silver image usually in the presence of physical development nuclei. For this purpose, a silver halide emulsion layer imagewise exposed is arranged or is brought in contact with an image receiving layer in the presence of a developing agent and a silver halide complexing agent to convert unexposed silver halide to a soluble silver complex salt.
At the exposed area of the silver halide emulsion layer the silver halide is developed (chemical development) and so is no longer dissolved and cannot diffuse.
At the unexposed area of the silver halide emulsion layer the silver halide is converted to a soluble silver complex salt and is transferred into the receiving layer, where it forms a silver image usually in the presence of physical development nuclei (e.g., heavy metals or sulfides thereof).
The actions of silver halides at exposed and unexposed areas are reverse in direct positive silver halide emulsions.
It is well known that rapid formation of transfer silver is necessary for obtaining transfer silver images of high contrast and high sharpness in image receiving layer. The rapid formation of transfer silver is performed by rapid development of transferred silver complex salt, e.g., silver thiosulfate complex salt, due to which said complex salt cannot diffuse in lateral direction in nuclei-containing image receiving layer.
Typical processing solutions used in DTR process contain at least silver halide complexing agents such as thiosulfates, alkaline substances such as sodium hydroxide, preservatives such as sulfites and developing agents such as hydroquinone and 1-phenyl-3-pyrazolidone.
However, these high alkali processing solutions containing the developing agent have the defect that said developing agent undergoes air-oxidation to lose its effect and it is known that this defect can greatly be improved by incorporating the developing agent in DTR materials, namely, in the silver halide emulsion layer and/or hydrophilic colloid layers which are permeable to water through to or out from the silver halide emulsion layer.
In the case of such diffusion transfer materials containing developing agent, alkali activating solutions containing no or substantially no developing agent are generally used.
Japanese Patent Publication (Kokoku) No. 27568/64, No. 30856/72 and No. 43778/76 may be referred to regarding DTR process which uses alkali activating solutions.
According to these patent publications, dihydroxybenzene compounds and 3-pyrazolidone compounds as developing agent are used in an amount of at least 50 mg, preferably 100 mg to 5 g per 1 m.sup.2 of light sensitive material.
However, even if the developing agent is incorporated in a silver halide emulsion layer or nonlight sensitive layers such as protective layer, intermediate layer, undercoat layer, etc., the oxidation of the developing agent with air cannot be completely avoided and as a result there occur undesired effects such as reduction of developing speed, decrease of sensitivity, reduction of contrast and density of silver images, occurrence of fog, etc.
The loss of effect of developing agent is caused by not only oxidation with air, but other factors, one of which is carbon black.
It is well known that carbon black is useful as a pigment for preventing halation, but it is also well known that carbon black causes fogging of silver halide photographic materials during storage [see, e.g., Japanese Patent Publication (Kokai) No. 68520/75]. Furthermore, when the photographic materials stored contain carbon black contacting with developing agents such as 1-phenyl-3-pyrazolidone, the greater fog occurs to result in reduction of density and gradient of silver on image receiving elements which is obtained by diffusion transfer development and decrease of transfer speed.
The occurrence of much fog brought about by coexistence of carbon black and 1-phenyl-3-pyrazolidone is due to promotion of the defect of either one of the two, but it is not known which defect is promoted.
Another disadvantage of incorporation of developing agent in DTR materials is due to the large amount of developing agent incorporated. That is, the amount of developing agent usually contained in DTR materials is about 5 times (per one unit of silver halide) that of the developing agent usually contained in DTR processing solutions. This fact indicates necessity to consider any inefficient utilization of developing agent, limitation in content of developing agent, unfavourable effect of excess developing agent, etc.
However, use of developing agent, especially, 3-pyrazolidone in an amount of less than about 50 mg/m.sup.2 in combination with inefficient utilization thereof increases dependence on processing temperature of DTR processing solution and, for example, there is the defect that contrast decreases by processing at low temperatures such as 10.degree.-15.degree. C. This decrease of contrast sometimes causes formation of yellowish brown silver images in image receiving layers even with use of blackening agents such as 1-phenyl-5-mercaptotetrazole.